1. Field of the Invention
The present invention relates to a method of removing hard masks on gates, and more particularly, to a method of uniformly removing hard masks on gates.
2. Description of the Prior Art
The performance of an electrical device is affected by the size of various features in the device, as well as the device switching speed and power consumption. As semiconductor devices continue to decrease in size, there is a desire to replace a conventional polysilicon gate electrode with a metal gate electrode to further improve device performance. There are challenges, however, to implementing such features and processes in conventional fabrication.
Before the polysilicon gate electrode can be replaced, a cap layer on top of the polysilicon gate electrode must be removed. Differences in topography of the substrate or differences in the pattern densities may cause the cap layer to be removed unevenly, so that some polysilicon gate electrodes are exposed while others are still covered by the cap layer. The exposed polysilicon gate electrodes will have a lower height than the polysilicon gate electrodes still covered by the cap layer, making them susceptible to damage from subsequent processes. Furthermore, the different heights of the polysilicon gate electrodes will cause the metal gate electrodes formed afterwards to have different heights.